Solvent extraction



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INVENToRs: William Hqz/zi/ce Robert E. Wilson Fr erick M/aliioczmfz' www Patented July 6, 1937- UNITED STATES PATENT oFFlcE soLvENT Ex'rnAorroN Application May '29, 1934,y Serial No. 728,138

17 Claims. (Cl. 196-13) This invention relates to improved methods and means for fractionating hydrocarbon oils by means of solvents and it pertains more particularly to the fractionation of lubricating oil stocks into paraiiinic oils, naphthenic oils' and asphalts, the last two being sometimes withdrawn as a single fraction.

An object of our invention is to minimize solvent requirements and to minimize solvent losses. A further object isvto provide apparatus which can be built and.. operated at a minimum expense. A further object is to provide a system which will give maximum yields of oils of good color, low carbon residue, resistance to oxidation and sludging, and high viscosity index, or, in

` other words, which will insure a sharp separation between desirable paraiilnic fractions and less desirable naphthenic fractions. A further object is to provide a combined deasphalting and solvent extraction system wherein the optimum temperatures and optimum proportions of oil to solvents will be employed in every stage throughout 'the entire system. A further object is to use the heat from a high temperature propane deo asphalting stage to ash propane from an intermediate rainate prior to its introduction to the following stage. Also, our object is to remove propane from stage to stage as we approach the admission of fresh solvent into the system and to effect a temperature increase simultaneous with this removal of propane. A further object is to return depropanized oils from an extract treating system to a solvent extraction system at a point above the main oil feed, so that the added oil will be of about the same paraflinicity as the oil in the system. Other objects will be apparent as the detailed description of our invention proceeds.

Our invention relates primarily to the use of at least two different solvents, one of them preferentiallyY dissolving naphthenic oil. components and the other dissolving paraiiinic oils and rejecting c olor bodies and high molecular weight asphaltic compounds. The solvent for dissolving naphthenic components may be phenol, cresol (cresylic acids, ortho, meta, para and mixtures thereof), coal tar and wood tar acids usually associated with phenol and/or cresol, pyridine, furfural, nitrobenzene, aniline, chloraniline, benzaldehyde, benzonitrile, chlorphenol, nitrotoluene, phenyl acetate, dichlorethyl ether; sulfur dioxide, etc. and/or mixtures of one or more of any of these compounds. Our other solvent is preferably a light hydrocarbon such as ethane, propane, butane., isobutane, pentane,

hexane, with perhaps some propylene, butylene, etc. or mixtures of one or more of said hydrocarbons. Such hydrocarbons or mixtures thereof (except hexane and perhaps pentane) may generally be described as liquefied normallygaseous hydrocarbons and for our purposes they should usually have a vapor pressure between those of propane and butane. It should be understood, however, that we do not limit ourselves to the use of light hydrocarbons as supplementary solvents to the solvents for extracting naphthenic components. We prefer to usepropane, but we may employ any light solvents which are equivalent to the propane in its property of precipitating asphalt and treating parafiinic oil out ofv extract material.

Our invention is based on the results of a vast amount of research'which has established certain fundamental principles that were heretofore not known and our invention resides in the utilization of these fundamental principles and their application in practical solvent refining processes and apparatus.

More specifically, .we have found that propane can beused to precipitate asphalt from an asphalt-bearing oil, that the propane precipitates the extremely high ,molecular weight components of the oil whether'naphthenic or paramnic, and that at high temperatures lof fromabout 140 to 200 F. the deasphalting action of propane is suflicient to remove a large portion of the color bodies to yield an oil of extremely low carbon residue or Conradson carbon and one which requires a very small amount (if any) of clay for finishing. By- "high temperatures we mean temperatures within about 50 or 60 F. of the critical temperature o f the light hydrocarbon solvent (propane, butane, ethane, etc.).

We have found that many of the popular novtions as to the virtue of propane in countercurrent extraction processes are in error; particularly we have found that propane -is undesirable in that portion of a solvent extraction process wherein the fresh solvent is introduced and the final raffinate is withdrawn; if propane is permitted to remain in the system at these points,

an unduly large amount of the naphthenic solvent will be required, which in turn means that solvent losses will be greater and that equipment costs will be greater, and at the same time fractionation is not as sharp as when propane is removed from the system.

We have found that propane may be used to excellent advantage to throw paraiilnic oil out of solvent-extract mixtures, particularly when the oil stock is extremely naphthenic (Gulf or West Coast oils).

In practicing our invention .we preferably subject asphalt-bearing residuur to a countercurrent propane-deasphalting step, the oil being rst deasphalted at temperatures between to 200 F. to remove practically all of the coloring matter and carbon-forming bodies from the parainic and naphthenic oils. 'I'he rejected layer from the rst stage is again propane-deasphalted with fresh propane at a lower temperature to recover the valuable oils which were thrown out with the asphalt in the first stage and this recovered oil is then returned to said first stage. The light colored oil from the initial deasphalting stage is ashed to remove a substantial portion, if not all, of the propane and the depropanized light colored oil is then countercurrently extracted with the naphthenic solvent. The extract from the countercurrent extraction of the deasphalted oil is treated with propane, preferably in the presence of solvent, and the parainic oilwhich is recovered from the extract is returned to the main countercurrent extraction system and preferably at a point above the main oil inlet.

Our invention is capable of many modications; it may be used on any type of oil whether distillate or residue, no matter what its source, viscosity, or chemical characteristics. It may also be `used on synthetic oils, oils obtained from shale and from brown coal tars, oils produced by hydrogenation and, in fact, any mixture of parafflnic and naphthenic oil components.

The invention will be more fully understood from the following drawings which form a part of this specification, in which similar parts are designated by like reference characters throughout the several views and in which:

Figure 1 is a miscibility diagram of a threecomponent solvent extraction system: oil, propane and anhydrous cresylic acid; the oil in this case is a distillate having a viscosity of 1051` seconds, Saybolt universal, at 210 F. and made lfrom Mid-Continent crude; Figure 2 is a miscibility graph showing effect,

of varying amounts of propane on miscibility temperature of a 50 :50 mixture of said oil and anhydrous. cresylic acid (vertical section on line zebmP of Figure 1) Figure 3 is a ow diagram showing a preferred outline of our process;

Figure 4 is a flow diagram to represent highy temperature propane treating and deasphalting at an intermediate stage with counter-current extraction of depropanized asphalt-free oil;

Figure 5 is a ow diagram to represent a multistage counter-current system with increasing temperatures of propane treating and deasphalting followed by increasing but lower temperatures of counter-current extraction in the presence of diminished amounts of propane; and

Figure 6 diagrammatically represents another embodiment of our invention wherein the deasphalting and treating of the extract are carried out in separate systems.

It will be noted that Figures 3, 4 and 6 represent the process as carried out in continuous countercurrent towers or horizontal extractors wherein the solvent flows through the system in one direction and the oil flows through in the opposite direction. Figure 5 represents a multistagefsystem wherein the solvent and oil are mixed and settled to form intermediate extracts and/or rainates which are inturn mixed with rainates from prior stages or extracts from later stages, respectively. It should be understood, of course, that for the purposes of our invention we contemplate the use of multi-stage batch countercurrent'apparatus in the systems of-Figures 2, 3 and 5 where such apparatus oiers suificient,

advantages in temperature control, pressure control, phase separation, etc.

Three-component systems It will be noted that in certain stages of our Aprocess we must consider the mutual effect on n each other of the three components; oil (including parainic, naphthenic and sometimes asphalt), solvent, and light hydrocarbon. In our preferred example we will discuss the case of an S. A. E. d50, Mid-Continent distillate seconds Saybolt universal viscosity at 210 F.) extracted with anhydrous cresylic acid wherein propane is used as a deasphalting agent. A threecomponent chart of such a system is shown in the triangular diagram of Figure 1. Point X represents 100% cresylic acid; point Y, 100% oil; and point-P, 100% propane. Points along the line YX represent ratios of oil to cresylic acid in vthe absence of propane; along YP represent the proportion of propane to oil in the absence of cresylic acid; and along XP represent cresylic acid to propane in the absence of oil. Any point within the triangle represents a three-component system, the fraction for any component being the .ratio of the length of the perpendicular line from the point under consideration to the boundary opposite the apex for that component, divided by the altitude of the triangle. Thus, point lc represents a mixture of 50% oil, 30% propane and 20% cresylic acid.

This mixture of components may be in one, two or three separate liquid phases depending upon the proportions of various components and the temperature of and pressure on the mixture. Our solvent extraction process depends on the presencev of two liquid phases although a separate asphalt phase may sometimes be present as l a part of the extract. In the-studyof this problem we have determined innumerable miscibility temperatures,those temperatures at which the system changes from one to two liquid phases and vice Versa with slight alteration of temperature.

Thus the miscibility temperature of point k may be 30 F., of point m may be 80 F., of pointsr may be 100 F., of point t may be 120 F., etc. After obtaining this mass of information concerning miscibility temperatures, we connected all points having an equal miscibility temperature and for 80 F. we obtained lines abc and lmn. We flnd .that all components falling under the shaded areas bounded by these lines form two sent systems having miscibility temperatures higher than 80 F. and that the miscibility temperatures increase toward the sides of the triangle which form one boundary of` the shaded area. If we are considering a mixture containing equal parts of oil and cresylic acid with varying amounts of propane or, in other words, if we travel alongthe line zebmP we find that as more and more `propane is` added the miscibility temperatures rst decrease then increase and nally decrease again. This is clearly brought out by Figure 2.

It is usually desirable to operate solvent extraction processes at or slightly above room temperatures,about 80 to 100 F. Lower temperatures require expensive refrigerationand are complicated by wax separation, whlle higher temperatures result in undesirable and unnecessary heat losses. If only a small amount of propane is added to any composition in shaded area abc (Figure 1), the resultingcomposition will be displaced toward P or, in other words, it will result in a decrease in miscibility temperature, which is undesirable. This fact is shown more clearly in Figure 2 wherein the same points are represented by the same letters and wherein percent propane is plotted against miscibility temperature. If4 propane is added anywhere to the left of w or w', the miscibility temperature is lowered, but if it is added between points w and r-themiscibility temperature is increased or in other words phase separation is favored.

When very large amounts of cresylic acid are used, particularly with naphthenic oils, the miscibility temperature of the mixture becomes so low that phase separation in the absence of propane is impossible at temperatures of F. For instance, point a in Figure 1 represents a mixture of which the miscibility temperature is just 80 F. If propane is added to this mixture, the miscibility temperature of the three-component system will be as illustrated by the dashed line, from which it will be seen that at least 35% propane is necessary to effect phase separation at temperatures higher than 80 F., optimum operating mixtures containing :from Sil-80% of propane. Theuse of propane is most desirable here because it gives very high misci-` bility temperatures.

In practice we do not employ as much as 97 parts cresylic acid to 3 parts of oil, but we have discovered that naphthenic oils have the same effect as additional amounts of cresylic acid in lowering the miscibility temperature. In other words, the cresylic acid-extract produced in our extraction process may be entirely miscible at 80 F. in any proportion and it will exhibit the characteristics of the dashed-line curve in Figure 2 at higher concentrations of oil than shown for the dashed line in Figure 2. To obtain further phase separation for recovering additional parafiinic oil from this extract, it is necessary to add a considerable amount-of propane to the mixture to throw the-composition in the double cross-hatched area.

Cresylic acid raffinate, on the other hand, will correspond more nearly to the conditions shown by the dotted lines or the dot-dash lines of Figures 1 and 2. In this case it will be seen that the maximum miscibility temperature and, therefore, maximum phase separation will be obtained in the absence of propane. No amount of pro.- pane will throw the miscibility temperature of a 6:4 oil-creso1 mixture in the desired operating range on the right hand side of Figure 2.

In extracting any given crude with any given solvent, we have found that an amount of propane should be used which will give the highest miscie bility temperature with the minimum required a line amount of solvent. This amount of propane may be determined by making preliminary experiments to obtain curves corresponding to those shown in Figures 1 and 2 and then regulating the amount of propane in each stage of the extraction process to obtain the maximum miscibility temperature in that stage. The optimum amount of solvent is usually about 1 to 3 parts per part of .oil. In the final raflinate stages propane should be absent. Enough propane should be employed in the remaining stages to shift the composition of the mixture to the region y of maximum miscibility temperatures, as indicated by the double cross-hatched area in Figit decreases the unavoidable loss of solvent in the recovery of it from resulting extracts and railinates.

v While still on the subject of the miscibility diagram,'we should point out that this diagram is not the same for all crudes and that the naphthenic components of a crude behave much the same way in a system as the cresylic acid as -far as miscibility is concerned. lIf a solvent concentration is increased beyond a certain point the miscibility. temperature is lowered; likewise if the proportion of naphthenic materials in the oil is increased beyond a certain point the miscibility temperature is lowered. The addition of propane is desirable in the first Istages of the countercurrent extraction of the railinate whenever the propane tends to increase the miscibility temperature because this promotes phase separation. It is desirable to remove the propane or at least a large portion of it before the nal vcontacting of ranate with fresh solvent because this nal rainate will be paraiilnic in character.

. Deasphalting-Solocnt emtractzon Y In Figure 3 we have shown how the phenomena of propane deasphalting can be utilized with 'great effectiveness in our solvent extraction system. Oil feed from line I0 is deasphalted in the single stage unit II by means of propane which is introduced through lines I2 and I3. The propane introduced through line I2 contains paraffinic oil which has been removed from the extract in countercurrent system I4, the propane being introduced thereto through pipe I5 and extract removed therefrom through pipe I6. The propane which is introduced into the deasphalting unit through `pipe I3 carries with it the propanesoluble oils from countercurrent deasphalting system I 1 to which propane is introduced through I8 and from which asphalt is removed through line I9. In this manner all of the good oils from both the asphalt and the extract are recovered and the propane which is associated with these oils is utilized in deasphalting incoming feed stock.

The propane-soluble oil from unit II is introduced through line 20 to propane still 2I wherein it is substantially depropanized and then passed by line 22 to countercurrent or multi-stage ralnate solvent extraction system 23. Solvent is introduced through line 24 and rainate withllo drawn through line 25. The solvent-extract mixture is transferred by line 26 to the countercurrent extract treating system I4., The asphalt from unit I I is transferred to countercurrent asphalt washing system I1, the asphalt finally being removed through line I9. It should be understood throughout this description that there may be propane and/or solvent in the streams leaving the system, bothv of which are to be recovered and re-used in accordance with well known practice.

An outstanding feature of this system is the recovery oi good (parafnic) oil from both the extract and the asphalt and the depropanizing of the railinate to prevent the presence of the propane in the countercurrent raiiinate extraction system. Another feature of thisprocessl is the double use of propane for washing purposes in countercurrent systems I4 and I1 and for deasphalting in unit II. however, that we may introduce the oil from line I2 directly into the countercurrent rainate' system, but in this case we prefer to remove propane therefrom, at least in the final stages of the rainate extraction system. Other modifications and expedients will be more clearly understood from the following-more detailed description.

Elevated temperature intermediate stage The use of propane for deasphalting is well known (Use of Propane in Lubricating Oil Reilning presented before American Petroleum Institute October 25, 1933, by Bray, Swift and Carr). It has also been discovered'that oil may be fractionated by means of propane at increased temperatures and pressures. A black oil may be soluble in propane at 80, but when this propane solution is heated under pressure to 150 a phase separation occurs, the black color bodies and asphaltic constituents forming a lower phase and a lower molecular weight paralinic oil forming the upper phase. As Ithis temperature increases to the critical temperature of propane, the black oil phase 1ncreases in volume and the propane phase becomes lighter and lighter in color, the oil remaining dissolved in the propane gradually assuming a lower viscosity, a lower carbon residue or Conradson carbon, and a lighter color. We may utilize this phenomenon in our solvent extraction. systemin two ways: We may employ the high temperature 'deasphalting step as a part of a countercurrent deasphalting vprocess prior to the solvent extraction, so that asphalt and color bodies will not contaminate the solvent extraction system, increase the diiculty of solvent recovery and/or increase the cost of claying orA nishing of ythe nal lubricant. When asphaltic material does find its way into a countercurrent solvent extraction system and propaneis used to wash the good (parafnic) oil out of the extract we utilize the high temperature deasphaltingin the presence of the solvent to throw out objec- -t' tionable color bodies and asphaltic materials and to thereby obtain the same advantages as those hereinabove indicated. In both casesA we may utilize the heat which is stored in the propaneoil mixture by the high temperature deasphalting step to distill the propane from the oil prior to the introduction of said oil into the solvent extraction system.

An example of the use of our high temperature propane wash at an intermediate stage is diagrammatically illustrated in Figure 4. Here the deasphalting and treating of the extract is ac-l complishedin the same apparatus, which appa- It should be understood,

ratus is designed to withstand pressures of from 500 to 1000 lbs. per square inch.` The oil is introduced through line I to pressure vessel 28 which is provided with a steam coil 29 or other heating means. The heating means may, of

course, be dispensed with if the incoming oil is.

of a sufficiently high temperature so that the resulting mixture will be at about 140 to 200 F.

-It will be observed that in this arrangement the deasphalting is accomplished simultaneously with the treating of the extract, so that line 26 leads directly from countercurrent system 23 to the hot propane precipitation pressure vessel 28 (which corresponds to single stage unit II of Figure 3) and asphaltic material together with solvents from pressurevessel 28 are conducted by pipe 21 to the countercurrent extract washing system I4. Since the intermediate stage is at high pressure we use a pump 30 in line 26, pres'-` sure-release valve 3I in line 20, a pump 32 in line I2, a pressure release valve 33 in line 21 and in addition we employa cooler 34 in line 21, so that undue pressures will not be built up in the countercurrent washing system I4.` We may, however, operate the propane washing stages or the entire system under the same pressure that prevails in high temperature stage 28. We prefer to maintain a temperature of about 140A to 200 F. in pressure Vessel 28 while we prefer to operate countercurrent raflinate system 23 and countercurrent extract system I4 at lower temperatures. It will be noted that yalthough a cooler 34 is employed in line 21, such a cooler is not necessary in line 20 because the heat in the parafnic oil-propane solution is used to distil or flash off the propane in still 2I, so that the depropanized oil entering they rainate extraction system through pipe 22 is not only sustantially free of propane, but it is also at the desired operating temperature. In fact the heat of the solution may not be suicient for propane removal and we may employ steam coils in depropanizer 2I, bringing the depropanized oil back to about 'Z0-80 F. by means of a suitable cooler.

To describe briefly the operation of the apparatus vshown in Figure 4, the' propane with its `good (parainic) oil from treating system I4 is passed countercurrent to the extract from extraction system 23. System 28 is vat so high a temperature and pressure (it may be called a pressure vessel) that there is no appreciable phase separation between parainic and naphthenlc constituents of the type illustrated in Figure 1, but there is a separation between the paraflinic-naphth'enic solutions and the asphaltic and color bodies which may have been carried from the extract system with the oil solution in line I2. Thus the propane-soluble fraction which .leaves pressure vessel 28 through line 20 is light 'colored and relatively free from asphalt and carbon-forming substance and-when it is depropanized in still 2| and extracted in rafnate system 23 an excellent railinate is obtained from line 25. At the same time a large amount of good (paraflinic) oil is thrown out of solution in pressure vessel 28 and this good oil is recovered in the lower temperature countercurrent propane washing system I4. f

We prefer to introduce the incoming feed stock directly into pressure vessel 28, so that as much .propane-soluble oil as possible may be introduced directly into the raffinate countercurrent system 23, thereby placing a smaller burden on countercurrent extract .Washing system I4 and making that system more ,eilicientt It should be understood, however, nthat the incoming oil may be introduced at one of the later stages of the extract treating system |4 or one of the earlier stages of the rainate countercurrent system 23.

Also, while we have shown the removal of propane at one point in still 2|, it should be understood that the propane may be removed at a later point in the countercurrent rafnate system or it may be reduced progressively as the oil progresses through said raffinate system toward the introduction of fresh solvent. I

As hereinabove stated, we will probably prefer to carry out our process in a continuous multistage countercurrent apparatus as diagrammatically illustrated in Figure 5. The process illustrated by this figure is fundamentally the same as that shown in Figure 4 and it may be described as follows:

Oil stock from line I is admixed with extract from a raffinate countercurrent system (from line 35) and raflinate from an extract countercurrent system (from line 36) and this entire mixture is introduced into high pressure separator 31 at a temperature of about 180 F. The various liquids may be mixed in suitable mixers and if necessary they may be passed through a heat exchanger.38 to bring them up to the required temperature. The extract layer from separator 31 is withdrawn through line 39 and admixed with rafhnate withdrawn from a preceding settler through pipe 40, the mixture being introduced at an intermediate point of settler 4|. This settler is preferably at a lower temperature, about 130 to 140 F., and the temperature of the settler may be controlled by means of the heat exchanger 42. Rafiinate from settler 4| is that which was hereinabove described as being withdrawn through line 36 for admixture with incoming oil stock. Extract from settler 4| is withdrawn through line 43 and admixed with incoming propane from line 44, the mixture being effected in a mixing apparatus 45 designed to admit the propane in small amounts and with suflicient agitation to prevent agglomeration of asphaltic materials. This mixture of propane with extract is introduced into settler 46 and final extract and asphalt are withdrawn therefrom through pipe 41. Settler 46 is preferably maintained at above room temperature and pump 48 may therefore be necessary to force raffinate from'settler 46 through line 40 to settler 4|. Likewise, pump 49 may be required to force raffinate from settler 4| through line 36 to the higher temperature settler 31. A pressure reducing valve 50 may be employed in line 39 and a pressure reducingvalve 5| in line 43. The entire system may be operated at a uniform high pressure. It will thus be seen that in thel countercurrent extract washing stages (which also act as deasphalting stages) there is a constant decrease in temperature from th'e entrance of the oil stock to the withdrawal of the extract.

In the upper part or railinate countercurrent section the temperatures are lowered sufliciently -to effect phase separation. In this case the lowv maintained at a temperature of about '10 F. It 75 may be maintained at this temperature by steam coils in the settler, but preferably by heat exchanger 58 through which the incoming materials are passed.

Extract from settler 51 is forced by pump 53 through line 35 as hereinabove described. Ralnate from settler 51 is withdrawn through line 60 admixed with a solvent extract from line 6| and the mixture introduced into the center o! settler 62 preferably atyabout 80 F. If there is any propane in the rafllnate which is withdrawn in line 60, it may be removed by still 63 and the depropanized rafllnate may be mixed with extract 6| as hereinabove described. Here again` the temperature of the fluids entering the system may be regulated by heat exchanger 64. Extract from settler 62 is passed by pipe 56 to settler 51 as hereinabove described.

Finally, the raillnate from settler 62 is passed by line 65 to be admixed with incoming solvent through line 66, this mixture being settled in settler 61 at about 90 F. Any remaining propane may be removed by by-passing the ramnate in line 65 through still 68. Extract from set-l tler 61 is withdrawn through line 6| and ramnate is withdrawn from the system through line 69.

It may be desirable to gradually increase the temperature of the countercurrent raiilnate extraction system, in which case the heat means employed in stills 63 and 68 may furnish the necessary heat for increasing the temperatures of the final raffinate settling systems. However, our invention is not limited to a temperature variation in this part of the system except insofar as said temperature regulation is tied up with the removal of propane from the raiilnate streams. It will be understood, of course, that the lubricating oil stock may be introduced at a point nearer the extract end of `the system or nearer the raiilnate end of the system depending upon the nature of the stock introduced,` but as a general rule it is more desirable to introduce it at the high temperature stage.

The embodiment shown in Figure 5 contemplates the deasphalting and the treating of the residue in the same system, but if there is a large amount of asphalt in the oil stock we prefer to accomplish the deasphalting in a separate stage prior to the introduction of the oil into the apparatus described in Figures 4 and 5. In such cases a large amount of the propane necessary for the high temperature propane precipitation step, may be introduced with the paraftlnic-naphthenic oil mixture from the deasphalting step and the asphalt may `be recovered separate and As indicated in Figure 3 we prefer to remove the asphalt and the naphthenic oil in separate streams and our preferred embodiment is therefore indicated in Figure 6. The incoming oil from line I0 meets a propane solutionfrom line 10 and the mixture is introduced into a high temperature high pressure vessel 1|. This ves--` sel corresponds to vessel 28 of Figure 4 and it may be heated by steam coil or the entering liquids may be passed through a heat exchanger. The exact temperature maintained in this vessel will depend somewhat on the nature of the oil undergoing treatment, but it should be sufcient to throw out all asphaltlc materials and objectionable color bodies.

'I'he precipitated oils and asphalt are withdrawn from pressure vessel 1| through line 12, pressure reducing valve 13 and cooler 14, after which they are mixed with another propane solution from line 15 and the mixture is introduced into deasphalting chamber 16. The railinate from chamber 16 is forcedV by pump 11 through pipe 18 as hereinabove described. The

extract from chamber 16 is withdrawn through pipe 18, mixed with propane from line 19, and introduced into deasphalting chamber 80. Asphalt is removed from the system through line 8| and the propane-solublematerial from chamber 80 is returned to the preceding stage through line as hereinabove described.

The light colored propane-soluble oil from the top of pressure vessel 1| is withdrawn through 15 line 82 and pressure reducing valve 83 to propane still 84 and the depropanized oil is introduced by `line 15 to countercurrent raiiinate extraction system 23.

The extract from the raffinate extraction system is withdrawn through line 86, mixed with a propane solution from line 81 and introduced into propane washing chamber 88. Since the extract is naphthenic in character and since there is a preponderance ,of solvent, the addition of the propane solution tends to promote further phase separation, so that much valuable parafflnic oil is removed from the solvent and extract material (note Figure 1 and above discussion thereof). The extract' from the base of chamber 88 is withdrawn through pipe 89, mixed with propane solution in pipe 98, and introduced into settling chamber 9|. 'I'he railinate from settling chamber 9| is passed by line 81 for admixture with incoming extract as hereinabove described. The extract from settler 9| is withdrawn through line. 92 and mixed with fresh incoming propane through line 93, the mixture being settled in chamber 94. Raillnate from chamber 94 is withdrawn through pipe 98 for admixture with prior extract material as hereinabove described. Naphthenic oil is removed from the system through line 95.

'Ihe propane solution of paraffinic materials which have been recovered from the extract is withdrawn from the top of settler 88 by pipe 96, depropanized in still 91, andpassed by pipe 98 to that portion of tower 93 in which the liquids have a corresponding paraiiinicity,-usually considerably higher in the tower than the introduction of deasphalted naphthenic charging stock.

We may avoid the necessity of depropanizing still 91 by passing the propane solution from settler 88 directly through pipe 99 by means of pump |08 to high pressure deasphalting vessel 1|. The propane thus introduced may facilitate the deasphalting step by supplying added amounts of propane and the slight amount' of solvent which is carried into the deasphalting step therewith may likewise facilitate phase separation and the removal of undesirable constituents. It should be noted that when line 99 is employed Figure 6 is substantially the same as Figure 3, but inv both of these cases it becomes necessary to remove solvent from the asphalt stream as well as from the naphthenic oil stream. Ordinarily, therefore, we prefer to return the propane solution from settler 88 directly back to the lating to S. A. E. 50 MC distillate, anhydrous cresylic acid and propane. Other oil stocks. solvents, and light hydrocarbons may be used in place of those hereinabove described. In such cases the curves will not be of exactly the shape as those shown in Figures 1 and 2, but they will be of the same general characterthey will show that light hydrocarbons like ethane and propane tend to promote phase separation in mixtures which are largely naphthenic, and tend to promote miscibility in mixtures which are more paraflinic. water (about 2%) in the cresylic acid greatly increases the tendency toward phase separation. Alcohols and other modiers may also be added for this purpose. Also mixed solvents including a halogenated solvent may be more effective than single solvents in color removal. In any case, however, the desirability or undesirability of propane will follow the general rule hereinabove stated.

In Figures 4, 5 and 6 we have shown the use of diierent pressures in the various propane f washing stages, but it should be understood that the entire system may be designed to operate under pressures of 350 to 2000 pounds per square inch.

In all of the systems .hereinabove described the `paraflinic oil has been separated from the extract in the presence of the solvent. We may, of course, distil the solvent from the extract and then admix the extract with incoming oil or we may subject the extract to a propane fractionation at high temperature or to a subsequent fractionation with diierent solvents either to produce an intermediate grade lubricating oil or to produce additional parahnic materials for introduction into the main rafiinate extraction system.

In the above description we have not attempted to describe all of the necessary pumps, valves, storage tanks, propane and solvent recovery systems, etc. Such features arewell known to those skilled in the art and their illustration on the drawings would tend to confuse rather than lclarify the invention. It should be understood, however, that we contemplated the use of pressure and temperature control devices, mixers, heat exchange features, etc. in accordance with sound engineering practice.

As hereinabove stated, an outstanding feature of our invention is the regulation of the amount of propane present in various parts of the system in order to obtain the desired miscibility temperatures and a sharp fractionation of parafiinic and naphthenic components. A further feature is the employment of a sufiiciently high temperacating oil stock containing asphaltic, naphthenic and paraiinic components which lcomprises treating said oil stock with propane at a temperature of about to 200 F. to separate asphaltic components from a propane solution of naphthenic and paraiiinic components, treating the asphaltic components with additional pro- The presence of smallamounts ol pane at a lower temperature to recover propanesoluble oils therefrom, returning said propaneso1ubleoi1s together with propane to the high temperature propane treating step whereby the 5 recovered propane-soluble oils arecombined with propane-soluble naphthenic and paraflinic components separated in the rst step, removing propane from the paraflinic and naphthenic 'ccmponents, and separating the paraiiinic from the naphthenic components by means of a naphthenic oil solvent.

2. The method of claim 1 wherein the separation of the naphthenic from parainic components is effected countercurrently.

.i 3. The method of claim 1 wherein the naphthenic component is further treated with propane and wherein the propane-soluble material therefrom is admixed with the hot propane solution of naphthenic and parainic components from the high temperature separation step.

4. The method of refining a lubricating oil stock containing asphaltic, naphthenic and paraifinic components which comprises admixing said stock with a propane solution of material extracted from asphaltic components, effecting a phase separation of said oil-propane mixture at a temperature of about 140 to 200 F. to separate asphaltic components from the propane solution of paraiiinic and naphthenic components, treating said asphaltic components with propane to obtain the solution for the rst step of the process, removing propane from the mixture of naphthenic and paramnic components, and cooling the mixture to a temperature of about 70 to 100 F., countercurrently extracting said mixture with a naphthenic solvent, and separately recovering asphaltic components, naphthenic components,

and parafnic components from adrnixtures of the same with propane and naphthenic solvents.

0 5. The process of claim 4 ,wherein the naphthenic components from the solvent extraction step are treated with propane and wherein the propane solution from said treatment is admixed with the propane solution of paranic and naphthenic components prior to the removal of propane therefrom.

6. The method of refining a lubricating oil stock containing parafllnic, naphthenic and asphaltic components which comprises treating 0 said stock with propane at a temperature of about 140 to 200 F., removing propane from the mixture of parainic and naphthenic components, countercurrently extracting said depropanized mixture with a preferentially naphthenic solvent 5 to yield a parafiinic component and an extract,

countercurrently treating said extract with propane to 'yield a naphthenic -component and a propane-oil solution, countercurrently treating said asphaltic component with propane to yield 0 another propane-oil solution, and admixing both of said oil'and propane solutions with incoming oil stock for said propane treatment thereof at about 140 to 200 F.

7. The .method of refining a lubricating oil 5 stock which comprises admixing said stock with propane, heating said mixture to a temperature of 140 to 200 F. under pressure sufficient to maintain the propane in liquefied condition whereby a propane phase and a heavy oil phase are formed,

treating said heavy oil with propane at lower temperatures andreturning said propane with propane-soluble material tc the higher temperature higher pressure fractionation step, removing propane from the propane-oil solution formed in 75 the high temperature high pressure step, and

simultaneously lowering the temperature of said oil to about 70 to 100 F., and extracting said oil with a preferentially naphthenic solvent.

8. The method of claim 7 wherein the naphl thenic solvent from the solvent extraction step is introduced into said high temperature high pressure propane treating step. l

9. 'I'he method of refining a lubricating oil stock containing asphaltic, naphthenic and paraiiinic components which comprises mixing said stock with a light hydrocarbon which has been used to recover paraiiinic oils from mixtures thereof with other materials, subjecting said light hydrocarbon solution and oil stock to a temperature within about 60 F. of the critical temperavture of the light hydrocarbon under a pressure suicient to maintain the light hydrocarbon in liquid phase whereby two liquid phases are formed, separating the lighter liquid phase from the heavier liquid phase at said temperature, separating the paraiiinic from the naphthenic components in at least one of said liquid phases by means of a naphthenic solvent in a plurality of stages, and using different proportions of light` hydrocarbon diluent in said stages for obtaining phase separation in said stages.

10. The method of refining a lubricating oil stock containing naphthenic, parafnic and asphaltic components which comprises treating said oil stock with propane at a temperature of about 140-200" F. and at a pressure suicient to maintain the propane in liquid state whereby a propane-soluble fraction is separated from apropane-insoluble fraction, treating the propane; insoluble fraction with further amounts of propane at lower temperatures to recover propanesoluble fractions therefrom, returning said propane-soluble fractions to said rst-named step, reducing the pressure on the propane-soluble fractions from the first-named step whereby propane is removed from'the solution and the temperature of the solution is lowered to below 100 F., countercurrently extracting the cooled depropanized solution with a naphthenic solvent to form a rafiinate and an extract, treating said extract with propane to increase the miscibility temperature of the oil-solvent mixture and cause further separation of parafnic oil in propane solution, removing propane from said solution, introducing said depropanized solution to said countercurrent extraction system, and removing pro- .pane fromthe asphalt, raffinate and extract and removing solvents from the rafiinate and extract. 11. The combination of claim 10 wherein the depropanized 'solution from the treating of the extract is introduced into the counter-current solvent extraction system at a point at which its parafinicity is the same as the parainicity of the rafiinate in said system.

12. The method of refining mineral lubricating oil stocks which comprises introducing said stock into a high temperature zone maintained at a temperature of at least 140 F. and a pressure sufcient to keep propane liquid at said temperature, .introducing a selective solvent into an extraction zone, introducing extract solvent solution from the extraction zone to the high temperature zone, introducing propane into said high temperature zone, removing paraiiinic material from said high temperature zone to a depropanizing zone and from said depropanizing zone to said extraction zone, removing raiinate from said extraction zone and removing solvent-extract solution from the high temperature zone.

13. The method of claim 12 wherein the solvent comprises a phenolic liquid of the class consisting of phenols, cresols, cresylic acid, and coal tar and Wood tar acids associated with phenol.

14. The method of refining lubricating oil stocks which comprises extracting said stocks with about 1 to 3 volumes of a selective naphthenic solvent, introducing propane into the extract end of the system between the point at which the oil is introduced and the point at which extract is removed, whereby the miscibility temperature of the solvent-extract mixture is modied to release parainic oil, maintaining the oil-propane-solvent mixture at a temperature of atleast about 140 F. and a pressure suilcient to keep the propane in the .liquid phase at the point of oil introduction, maintaining lower temperatures in the raiinate and extract ends of the system, respectively and removing propane from the ralinate end of the system between the point of introduction of said lubricating oil stock and the point of introduction of the selective solvent, whereby the miscibility temperature is again altered to cause liberation of paranic oil from the solvent and to cause solution of naphthenic material therein.

15. The method of refining mineral lubricating oil stock containing asphaltic, naphthenic and parainic components, which comprises introducing said stock into a high temperature propane treating zoneat a pressure suilicient to keep the propane in a liquid state, introducing a selective solvent into an extraction zone, transferring solvent-extract solution from the extraction zone to a propane treating zone at a lower temperature than the first-named propane treating zone, introducing propane into said low temperature treating zone and removing solventextract material' therefrom, transferring propane solution from said lower temperature propane treating zone to said high temperature treating zone to furnish the propane therefor, removing paranic material from said high temperature zone to a depropanizing zone and from said depropanizing zone to said extraction zone, andv removing railnate from said extraction zone.

16. The method of rening a lubricating oil stock containing asphaltlc, -naphthenic and paraflinlc constituents which comprises introducing said stock into a high temperature propane treating zonefor separation of asphaltic com-l ponents, transferring the asphaltic components to a lower temperature propane treating zone and introducing propane into said zone for recovering parailinic and naphthenic components from said asphaltic components, withdrawing asphalt from said lower temperature zone, introducing the propane solution from the lower to the high temperature propane treating zone to furnish propane therefor, transferring the propane solution from the high temperature zone to a depropanizing zone and utilizing the sensible heat of the solution to furnish the latent heat of evaporation of propane whereby the depropanized solution is cooled to about '70 F. to 100 F., extracting said depropanized solution with a selective solvent in proportions to eilect separation of naphthenic from parainic components at said temperatures of about F. to 100 F., and separately removing asphalt, raffinate and extract from the system.

17. The method of claim 16 which also includes the steps of transferring the extract solution from the solvent extraction zone to a propane treating zone, adding propane to said material in said zone for dissolving .paraillnic material from the extract, removing extract solution from saiq propane-treating zone, depropanizing the solution of paraiinic components and returning said 1 parafnic components to said extraction zone.

WILLIAM H. BAHLKE. FREDERICK W. SULLIVAN, JR. ROBERT E. WILSON. 

